Torus-like Structure Research Articles

Iron Kα echoes from the circumnuclear disk orbiting Sɡr A⋆

Context. Molecular clouds in the Galactic center (GC) reprocess radiation from past outbursts of nearby high-energy sources, generating a bright Fe Kα fluorescence at 6.4 keV. The closest clouds to the GC are only ≃1.5 pc from Sgr A⋆, forming a torus-like structure known as the circumnuclear disk (CND). The study of fluorescence emission can lead to a characterization of the illuminating source(s), the reflecting clouds, and the global geometry of such a system lying in the GC. Aims. The primary purpose of our study is to analyze possible fluorescence signals arising in the CND. This signal would allow us to constrain the CND’s physical properties and the source-reflector system’s geometry. Methods. By exploiting the last ≃20 yr of XMM-Newton observations of the GC, we studied the variability of the Fe Kα line in the region around Sgr A⋆. We identified regions with a flux excess and computed the spectrum therein. We then derived the hydrogen column density of the CND after relating the intensity of the 6.4 keV line to the total energy emitted by known transient sources in the region. Results. Starting from data collected in 2019, we find significant line excesses in a region compatible with the eastern portion of the CND. The echo radiation can be linked to the 2013 outburst of the magnetar SGR J1745-2900. We derive a mean effective hydrogen column density of the CND in the eastern region of ≃1023 cm−2. Conclusions. The scenario depicted is physically plausible, given the luminosity, the position of the illuminating source, and the expected density of the CND. Further observations could link the variability of the echo signal to the light curve of the illuminating source. In this way, it would be possible to characterize the cloud response to the radiation front, achieving a more accurate estimate of the cloud parameters.

The properties of the AGN torus as revealed from a set of unbiased NuSTAR observations

The obscuration observed in active galactic nuclei (AGNs) is mainly caused by dust and gas distributed in a torus-like structure surrounding the supermassive black hole. However, the properties of the obscuring torus of an AGN in X-ray have not yet been fully investigated because of a lack of high-quality data and proper models. In this work, we perform a broadband X-ray spectral analysis of a large, unbiased sample of obscured AGNs (with line-of-sight column density 23 ≤ log(NH) ≤ 24) in the nearby Universe for which high-quality archival NuSTAR data are available. We analyzed the source spectra using the recently developed borus02 model, which enables us to accurately characterize the physical and geometrical properties of AGN-obscuring tori. We compare our results obtained from the unbiased Compton-thin AGNs with those of Compton-thick AGNs. We find that Compton-thin and Compton-thick AGNs may possess similar tori, whose average column density is Compton thick (NH, tor, ave ≈ 1.4 × 1024 cm−2), but they are observed through different (under-dense or over-dense) regions of the tori. We also find that the obscuring torus medium is significantly inhomogeneous, with the torus average column densities being significantly different from their line-of-sight column densities (for most of the sources in the sample). The average torus covering factor of sources in our unbiased sample is cf = 0.67, suggesting that the fraction of unobscured AGNs is ∼33%. We developed a new method to measure the intrinsic line-of-sight column density distribution of AGNs in the nearby Universe, and find the results to be in good agreement with constraints from recent population synthesis models.

APPLICATION OF PLASMA-ELECTROLYTE COATINGS ON TITANIUM WITH REFRACTORY METALS FOR DETOXIFICATION OF ENVIRONMENTS FROM POLLUTING SUBSTANCES

Based on the review of the peculiarities of the photocatalytic processes, the peculiarities of the catalytic action of oxide systems based on titanium dioxide are determined. It is shown that TiO2 is one of the most chemically and thermally stable and non-toxic inorganic oxides of semiconductors, whose photocatalytic activity is manifested by irradiation with ultraviolet part of the spectrum (λ 320–400 nm) and allows the oxidation of a significant amount of toxic agents to water and carbon dioxide. The essence of the photocatalytic process of oxidation of toxicants under the action of UV radiation on the TiO2 surface is considered. The proposed technology of photocatalytic detoxification of contaminants is economically available, environmentally friendly and allows its widespread use, in particular for autonomous systems, including dual purpose. It is established that the main requirements for materials for photocatalysis are their chemical and biological inertness, photocatalytic stability and activity, low cost. It is shown that the most rational technological form of the photocatalyst is the application (synthesis) of the catalytic layer on structured metal substrates, in particular titanium alloys. It is proved that these catalytic oxide systems can be effectively formed by the method of plasma-electrolyte oxidation in aqueous electrolytes with the addition of dopant metal compounds that increase the photocatalytic activity of the obtained heterooxide systems. It is proposed to use tungsten oxides of variable valence as the target additive. The kinetic regularities of the process of plasma-electrolytic oxidation of titanium VT1-0 in a diphosphate-borate electrolyte with the addition of tungstates have been studied. It is shown that in an electrolyte of this type at a current density of 1.0 A/dm2 in the galvanostatic mode for 30 min a uniform coating of TiO2·WxOy with a tubular torus-like structure and tungsten content of 2.5–7.5 wt.% is formed. The predicted quantitative composition of the heteroxide layer in combination with the surface morphology creates the preconditions for high catalytic activity of the synthesized coating for detoxification of media from anthropogenic pollutants.

<p><strong>Two new species of <em>Clusia</em> sect. <em>Cordylandra</em> (Clusiaceae) from the <em>brejo de altitude</em> vegetation, plateau of Ibiapaba, Ceará, Brazil</strong></p>

Two new shrubby species of Clusia sect. Cordylandra are described and illustrated. The male flower of Clusia nogueirae presents an androecium forming a conical volcano-like synandrium around a well-developed pistillode covered with resin. The male flower of Clusia ibiapabensis, on the other hand, presents an androecium of free claviform stamens, forming a broad torus-like structure around a well-developed pistillode. The two species occur in regions of brejos de altitude in the plateou of Ibiapaba, Ceará state, northeastern Brazil.

Hydrodynamic regimes induced by nanosecond pulsed discharges in air: mechanism of vorticity generation

The mechanisms controlling the hydrodynamic effects induced by nanosecond pulsed discharges applied between two pin electrodes in air at atmospheric conditions are investigated experimentally and numerically. A cylindrical plasma kernel is formed between the electrodes during the discharge. After the discharge, schlieren images show that the cylindrical kernel evolves in different ways depending on the gap distance: (1) for short gap distances (), the cylindrical kernel collapses to form a torus-like structure. In this case, the flow field presents a significant source of vorticity; (2) for larger gaps (), the kernel retains its initial cylindrical shape and cools down primarily through heat diffusion. The objective of this work is to understand the mechanisms leading to the formation of these two hydrodynamic regimes. To this end, simulations were performed and compared with the experimental schlieren images. It is shown that the main source of vorticity is the baroclinic torque caused by the cylindrical blast wave that follows the fast energy addition during the discharge. Finally, a criterion is given to predict the occurrence of the two hydrodynamic regimes. This criterion is then validated against experimental results from the literature.

Gas infall and possible circumstellar rotation in R Leo.

We present new interferometer molecular observations of R Leo taken at 1.2 mm with the Atacama Large Millimeter Array with an angular resolution up to These observations permit us to resolve the innermost envelope of this star revealing the existence of a complex structure that involves extended continuum emission and molecular emission showing a non-radial gas velocity distribution. This molecular emission displays prominent red-shifted absorptions located right in front to the star typical of material infall and lateral gas motions compatible with the presence of a torus-like structure.

PSR J1119–6127 and Its Pulsar Wind Nebula Following the Magnetar-like Bursts

Abstract We present a Chandra Director’s Discretionary Time observation of PSR J1119–6127 and its compact X-ray pulsar wind nebula (PWN) obtained on 2016 October 27, three months after the Fermi and Swift detection of millisecond bursts in hard X-rays, accompanied by a ≳160 times increase in flux. This magnetar-like activity, the first observed from a rotation-powered radio pulsar, provides an important probe of the physical processes that differentiate radio pulsars from magnetars. The post-burst X-ray spectrum of the pulsar can be described by a single power-law model with a photon index of 2.0 ± 0.2 and an unabsorbed flux of 10−12 erg cm−2 s−1 in the 0.5–7.0 keV energy range. At the time of Chandra observations, the pulsar was still brighter by a factor of ∼22 in comparison with its quiescence. The X-ray images reveal a nebula brighter than in the pre-burst Chandra observations (from 2002 and 2004), with an unabsorbed flux of 10−13 erg cm−2 s−1. This implies a current X-ray efficiency of at a distance of 8.4 kpc. In addition, a faint torus-like structure is visible along the southeast–northwest direction and a jet-like feature perpendicular to the torus toward the southwest. The PWN is best fitted by an absorbed power-law with a photon index of 2.2 ± 0.5 (post-burst). While the pulsar can still be energetically powered by rotation, the observed changes in PSR J1119–6127 and its PWN following the magnetar-like bursts point to an additional source of energy powered by its high magnetic field.

Dust inflated accretion disc as the origin of the broad line region in active galactic nuclei

The Broad Line Region (BLR) in AGN is composed of dense gas ($\sim 10^{11}$ cm$^{-3}$) on sub-pc scale, which absorbs about 30 per cent of the ionising continuum. The outer size of the BLR is likely set by dust sublimation, and its density by the incident radiation pressure compression (RPC). But, what is the origin of this gas, and what sets its covering factor (CF)? Czerny & Hryniewicz (2011) suggested that the BLR is a failed dusty wind from the outer accretion disc. We explore the expected dust properties, and the implied BLR structure. We find that graphite grains sublimate only at $T\simeq 2000$ K at the predicted density of $\sim 10^{11}$ cm$^{-3}$, and therefore large graphite grains ($\ge 0.3$ $\mu$m) survive down to the observed size of the BLR, $R_{\rm BLR}$. The dust opacity in the accretion disc atmosphere is $\sim 50$ times larger than previously assumed, and leads to an inflated torus-like structure, with a predicted peak height at $R_{\rm BLR}$. The illuminated surface of this torus-like structure is a natural place for the BLR. The BLR CF is mostly set by the gas metallicity, the radiative accretion efficiency, a dynamic configuration, and ablation by the incident optical-UV continuum. This model predicts that the BLR should extend inwards of $R_{\rm BLR}$ to the disc radius where the surface temperature is $\simeq 2000$ K, which occurs at $R_{\rm in}\simeq 0.18 R_{\rm BLR}$. The value of $R_{\rm in}$ can be tested by reverberation mapping of the higher ionisation lines, predicted by RPC to peak well inside $R_{\rm BLR}$. The dust inflated disc scenario can also be tested based on the predicted response of $R_{\rm BLR}$ and the CF to changes in the AGN luminosity and accretion rate.

Structural Properties of Nonionic Monorhamnolipid Aggregates in Water Studied by Classical Molecular Dynamics Simulations

Molecular dynamics simulations were carried out to investigate the structure and stabilizing factors of aggregates of the nonionic form of the most common congener of monorhamnolipids, α-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-C10-C10), in water. Aggregates of size ranging from 5 to 810 monomers were observed in the simulation forming spherical and ellipsoidal structures, a torus-like structure, and a unilamellar vesicle. The effects of the hydrophobic chain conformation and alignment in the aggregate, role of monomer···monomer and monomer···water H-bonds, and conformations of monomers in the aggregate were studied in detail. The unilamellar vesicle is highly stable due to the presence of isolated water molecules inside the core adding to the binding energy. Dissociation of a monomer from a larger micellar aggregate is relatively easy compared to that from smaller aggregates as seen from potential of mean force calculations. This analysis also shows that monomers are held more strongly in aggregates of Rha-C10-C10 than the widely used surfactant sodium dodecyl sulfate. Comparisons between the aggregation behavior of nonionic and anionic forms of Rha-C10-C10 are presented.

Mid-infrared interferometry of 23 AGN tori: On the significance of polar-elongated emission

Context. Detailed high resolution studies of AGN with mid-infrared (MIR) interferometry have revealed parsec-sized dust emission elongated in the polar direction in four sources. Aims. Using a larger, coherently analyzed sample of AGN observed with MIR interferometry, we aim to identify elongated mid-infrared emission in a statistical sample of sources. More specifically we wish to determine if there is indeed a preferred direction of the elongation and whether this direction is consistent with a torus-like structure or with a polar emission. Methods. We investigate the significance of the detection of an elongated shape in the MIR emission by fitting elongated Gaussian models to the interferometric data at 12 um. We pay special attention to 1) the uncertainties caused by an inhomogeneous (u,v) coverage, 2) the typical errors in the measurements and 3) the spatial resolution achieved for each object. Results. From our sample of 23 sources we are able to find elongated parsec-scale MIR emission in five sources: three type 2s, one type 1i and one type 1. Elongated emission in four of these sources has been published before; NGC5506 is a new detection. The observed axis ratios are typically around 2 and the position angle of the 12 um emission for all the elongated sources seems to be always closer to the polar axis of the system than to the equatorial axis. Two other objects, NGC4507 and MCG-5-23-16 with a reasonably well mapped (u,v) coverage and good signal-to-noise ratios, appear to have a less elongated 12 um emission. Conclusions. Our finding that sources showing elongated mid-infrared emission are preferentially extended in polar direction sets strong constraints on torus models or implies that both the torus and the NLR/outflow region have to be modeled together. Especially also models used for SED fitting will have to be revised to include emission from polar dust.

ASPHERICAL NUCLEOSYNTHESIS IN A CORE-COLLAPSE SUPERNOVA WITH 25M☉STANDARD PROGENITOR

The problem of nucleosynthesis was studied within an aspherical supernova model. The explosive burning was computed in a star of 25 M ☉ initial mass on its final stage of evolution. The chemical composition of a presupernova was taken from realistic evolutionary computations. A piecewise parabolic method on a local stencil was applied to simulate the hydrodynamics of the explosion. The gravity was recomputed by a Poisson solver on a fine grid as the explosion developed. A detailed yield of chemical elements was performed as a post-processing step using the tracer particles method. The produced nuclei formed a layer-like structure enclosing large fragments of nickel and iron-group isotopes that were pushed away from the central region by an explosion along the polar direction. The light nuclei were preferentially moving along the equatorial plane forming a torus-like structure.

X-RAY OBSERVATIONS OF THE SUPERNOVA REMNANT CTB 87 (G74.9+1.2): AN EVOLVED PULSAR WIND NEBULA

Pulsar wind nebulae (PWNe) studies with the Chandra X-ray Observatory have opened a new window to address the physics of pulsar winds, zoom on their interaction with their hosting supernova remnant (SNR) and interstellar medium, and identify their powering engines. We here present a new 70 ks, plus an archived 18 ks, Chandra ACIS observation of the SNR CTB 87 (G74.9+1.2), classified as a PWN with unusual radio properties and poorly studied in X-rays. We find that the peak of the X-ray emission is clearly offset from the peak of the radio emission by ~100" and located at the southeastern edge of the radio nebula. We detect a point source - the putative pulsar - at the peak of the X-ray emission and study its spectrum separately from the PWN. This new point source, CXOU J201609.2+371110, is surrounded by a compact nebula displaying a torus-like structure and possibly a jet. A more extended diffuse nebula is offset from the radio nebula, extending from the point source to the northwest for ~250" The spectra of the point source, compact nebula and extended diffuse nebula are all well described by a power law model with a photon index of 1.1 (0.7-1.6), 1.2 (0.9-1.4) and 1.7 (1.5-1.8), respectively, for a column density N_H = 1.38 (1.21-1.57) x 10^22 cm^-2 (90% confidence). The total X-ray luminosity of the source is ~1.6 x 10^34 erg s^-1 at an assumed distance of 6.1 kpc, with ~2% and 6% contribution from the point source and compact nebula, respectively. The observed properties suggest that CTB 87 is an evolved (~5-28 kyr) PWN, with the extended radio emission likely a `relic' PWN, as in Vela-X and G327.1-1.1. To date, however, there is no evidence for thermal X-ray emission from this SNR, and the SNR shell is still missing, suggesting expansion into a low-density medium (n_0 < 0.2 cm^-3, assuming D = 6.1 kpc), likely caused by a stellar wind bubble blown by the progenitor star.

Rhythmic shape change of a vesicle under a pH gradient

A vesicle that exhibits oscillatory structural changes under a pH gradient is reported. This vesicle is composed of oleic acid and sodium oleate and appears to exhibit a stomatocyte-type or a seemingly double spherical shape initially. The inner water is located at one side of the double spherical structure (i.e., the swollen part). The other side of the vesicle is nearly free of water. When the diffusion of hydroxide anions causes a pH gradient, the double spherical structure rotates such that its swollen part faces the higher-pH side. After this event, a small hole in the center of the swollen part begins to open. The vesicle changes to a torus-like structure: the swollen part is formed at the periphery, and a disk-like part is formed in the central part of the torus. The shape change proceeds via the torus-like shape, and the vesicle closes again to form a double spherical shape with a curvature opposite to the initial curvature. At this stage, the swollen part faces the lower-pH side. After this event, the vesicle rotates back to its initial state, where the swollen part faces the higher-pH side. This rhythmic transformation repeats numerous times. The size of the vesicle remains nearly constant during these numerous transformations. Thus, this vesicle continuously generates mechanical work from a pH gradient. In this study, experimental observations under an optical microscope and a model for the transformation are reported.

What is shaping the planetary nebula K3-35?

AbstractK 3-35 is a very young planetary nebula (PN) with a characteristic S-shaped radio emission morphology. It is the first PN where water vapor maser was detected: the emission is located in a torus-like structure with a radius of 100 AU and also at the surprisingly large distance of 5000 AU from the star, in the tips of the bipolar lobes. Several mechanism have been proposed to explain the bipolar morphology of PNe, and in the case of K 3-35 we believe we may be observing several of them at the same time: i) a disk-like structure traced by the H2O masers, ii) a precessing bipolar jet probably due to the presence of a binary companion and iii) circular polarization in the OH 1665 MHz masers, which suggests the presence of a magnetic field. Additional observations and modeling are needed to establish what mechanisms are shaping K 3-35.

A novel probe for spatially resolved emission spectroscopy in plasmas

A novel diagnostic device is developed to obtain spatially resolved emission profiles in plasmas. A ceramic tube is immersed into the plasma and moved along its longitudinal axis. A lens located at the other end of the ceramic tube images light onto an optical fiber which guides the light to a detector. In the case that the plasma emission is detected within a negligible solid angle, simple differentiation of the measured signal yields spatially resolved emission profiles. For non-negligible solid angles, spatial resolution can still be obtained by a more sophisticated evaluation. The design of the probe and the underlying theory are presented. The arrangement of the optics is analyzed in detail. Measurements in an inductively coupled radio-frequency (RF) hydrogen discharge in a GEC cell at different RF powers, neutral gas pressures and axial probe positions are performed. The obtained radial emission profiles of the Balmer-α line exhibit a torus-like structure which reflects the structure of the induced electrical field of the antenna. Furthermore, the transition from H to E mode at lower powers is observed.Based on a corona equilibrium model excitation rates are calculated out of electron energy distribution functions measured by an RF compensated Langmuir probe. A comparison of measured emission profiles with calculated excitation rate profiles shows very good agreement. Integrated emission profiles obtained by camera images are Abel inverted and compared with profiles obtained by the optical probe. The comparison demonstrates the advantage of the optical probe.

ACTIVE GALAXY UNIFICATION IN THE ERA OF X-RAY POLARIMETRY

Active Galactic Nuclei (AGN), Seyfert galaxies and quasars, are powered by luminous accretion and often accompanied by winds which are powerful enough to affect the AGN mass budget, and whose observational appearance bears an imprint of processes which are happening within the central parsec around the black hole (BH). One example of such a wind is the partially ionized gas responsible for X-ray and UV absorption ('warm absorbers'). Here we show that such gas will have a distinct signature when viewed in polarized X-rays. Observations of such polarization can test models for the geometry of the flow, and the gas responsible for launching and collimating it. We present calculations which show that the polarization depends on the hydrodynamics of the flow, the quantum mechanics of resonance line scattering and the transfer of polarized X-ray light in the highly ionized moving gas. The results emphasize the three dimensional nature of the wind for modeling spectra. We show that the polarization in the 0.1-10 keV energy range is dominated by the effects of resonance lines. We predict a $5-25%$ X-ray polarization signature of type-2 objects in this energy range. These results are general to flows which originate from a cold torus-like structure, located $\sim 1$pc from the BH, which wraps the BH and is ultimately responsible for the apparent dichotomy between type 1 and type 2 AGNs. Such signals will be detectable by future dedicated X-ray polarimetry space missions, such as the NASA Gravity and Extreme Magnetism SMEX, GEMS.

A COLLIMATED, IONIZED BIPOLAR STRUCTURE AND A HIGH DENSITY TORUS IN THE PLANETARY NEBULA IRAS 17347–3139

We present observations of continuum (λ = 0.7, 1.3, 3.6, and 18 cm) and OH maser (λ = 18 cm) emission toward the young planetary nebula IRAS 17347−3139, which is one of the three planetary nebulae that are known to harbor water maser emission. From the continuum observations, we show that the ionized shell of IRAS 17347−3139 consists of two main structures: one extended (size ∼15) with bipolar morphology along P.A.= −30°, elongated in the same direction as the lobes observed in the near-infrared (NIR) images, and a central compact structure (size ∼ 025) elongated in the direction perpendicular to the bipolar axis, coinciding with the equatorial dark lane observed in the NIR images. Our image at 1.3 cm suggests the presence of dense walls in the ionized bipolar lobes. We estimate for the central compact structure a value of the electron density at least ∼5 times higher than in the lobes. A high-resolution image of this structure at 0.7 cm shows two peaks separated by about 013 (corresponding to 100–780 AU, using a distance range of 0.8–6 kpc). This emission is interpreted as originating in an ionized equatorial torus-like structure, from whose edges the water maser emission might be arising. We have detected weak OH 1612 MHz maser emission at VLSR ∼ −70 km s−1 associated with IRAS 17347−3139. We derive a 3σ upper limit of < 35% for the percentage of circularly polarized emission. Within our primary beam, we detected additional OH 1612 MHz maser emission in the local standard of rest velocity ranges −5 to −24 and −90 to −123 km s−1, associated with the sources J17380406−3138387 and OH 356.65−0.15, respectively.

Metal-Dependent Assembly of a Helical-[Co3L3] Cluster versus a Meso-[Cu2L2] Cluster with O,N,N′,O′-Schiff Base Ligand: Structures and Magnetic Properties

Self-assembly of a tetradentate ligand, N, N'-bi(salicylidene)-2,6-pyridinediamine (H 2L), with Cu(II) or Co(II), affords a dinuclear [Cu 2L 2] complex ( 1) or a trinuclear [Co 3L 3] complex ( 2), which were characterized by the single crystal X-ray diffraction study. The coordination geometry of the Cu (II) centers in 1 is between square planar and tetrahedral, with the ligand adopting a cis-cis conformation to give a centrally symmetric structure, which can be regarded as a mesocate. However, the coordination geometry of Co (II) centers in 2 is distortedly tetrahedral, and the ligand adopts a cis-trans conformation. The whole complex of 2 is of a pseudo- C 3 symmatrical, torus-like structure, which can be regarded as a circular helicate. Both the mesocate and the helicate exhibit expanded supramolecular structures due to elaborate intercomplex pi-stacking interactions. These two complexes were also characterized by element analysis, IR spectra, and TGA. To verify the stability of 2, ESI-MS was carried out on both the crystal and the powdered samples. Variable temperature magnetic susceptibility measurements reveal that both 1 and 2 display antiferromagnetic properties. DFT calculations were carried out on 1 to verify the antiferromagnetic coupling between intracluster metal centers.

HCO+ emission possibly related with a shielding mechanism that protects water molecules in the young PN K 3-35

AbstractWater maser emission has been detected only toward three planetary nebulae (PNe). In particular, in K3-35, the first PN where water vapor maser emission was detected, the components are located in a torus-like structure with a radius of 85 AU and also at the surprisingly large distance of 5000 AU from the star, in the tips of the bipolar lobes. The existence of these water molecules in PNe is puzzling, probably related to some unknown mechanism shielding them against the ionizing radiation. We report the detection of HCO+ (J = 1 − 0) emission toward K 3-35, that not only suggests that dense molecular gas (~105 cm−3) is present in this PN, but also that this kind of PN can enrich their surroundings with organic molecules.

An H2CO 6 cm Maser Pinpointing a Possible Circumstellar Torus in IRAS 18566+0408

We report observations of 6 cm, 3.6 cm, 1.3 cm, and 7 mm radio continuum, conducted with the Very Large Array, toward IRAS 18566+0408, one of the few sources known to harbor H2CO 6 cm maser emission. Our observations reveal that the emission is dominated by an ionized jet at centimeter wavelengths. Spitzer IRAC images from GLIMPSE support this interpretation, given the presence of 4.5 ?m excess emission at approximately the same orientation as the centimeter continuum. The 7 mm emission is dominated by thermal dust from a flattened structure almost perpendicular to the ionized jet; thus, the 7 mm emission appears to trace a torus associated with a young massive stellar object. The H2CO 6 cm maser is coincident with the center of the torus-like structure. Our observations rule out radiative pumping via radio continuum as the excitation mechanism for the H2CO 6 cm maser in IRAS 18566+0408.